Wideband limitations of ray-optical techniques in radiowave propagation prediction

Further growth of mobile communication systems and the provision of mobile multimedia services can only be achieved in the future through the use of sophisticated access schemes, some of which require wideband radio channel information for their planning (e.g. wideband DS-CDMA). The planning and deployment of spectrally efficient wideband wireless personal communication systems in turn requires a reliable and accurate propagation prediction tool. Such propagation tools need to be able to predict channel parameters such as coherence bandwidth, delay spread, etc. We present numerical calculations that demonstrate that errors can arise in the computation of the wideband channel response, particularly in the shadow and transition regions of diffracting obstacles. We endeavour to place a numerical bound on these errors for perfectly conducting obstacle simulations. The validity of the numerical work is partly supported through wideband power frequency response measurements taken in a simplified scaled-frequency model urban environment in the laboratory.